1. Field of Invention
The present invention relates to a system for interpreting multiple marks on a scannable sheet, such as a scannable sheet used for administering objective examinations or collecting survey information. Each response "bubble" on the scannable surface is evaluated relative to selected other response bubbles on the sheet, and a determination is made as to whether the evaluated bubble is to be interpreted as chosen (i.e., intentionally marked as a response) or unchosen (i.e., intentionally not marked as a response).
2. Description of Prior Art
Modern multiple choice examinations are administered by requiring each respondent or examinee to choose his or her answers on some variation of the well-known scannable answer form. One such scannable form 100 is shown in FIG. 1. The scannable answer form 100 includes space for a number of questions to be answered by marking response areas ("bubbles") corresponding to answer selections provided for each question. The same or a similar form can be used to collect survey information, where the respondent responds to survey inquiry questions by darkening response bubbles. Unlike the responses in typical academic examinations, the responses in surveys are not evaluated as "correct" or "incorrect," but discerning the respondent's intended responses is still equally important.
Whatever the purpose of the scannable form, there are normally at least two response bubbles in the answer area for each question, and often there are more than two. FIG. 1 shows five response bubbles 101 for each question (labeled "A" to "E"). In the context of a typical academic examination, the respondent or examinee indicates on the scannable form his or her answer to each question by darkening response bubbles. The test is graded by a procedure that involves scanning the form to obtain a read level for each response bubble, which indicates how dark the examinee's mark is for that particular response bubble. Read levels are usually scaled in the range of 0 to 15, where a higher read level indicates a darker mark, and a lower read level indicates a lighter mark (level 0 being the lightest, 15 the darkest). If an examinee does not mark a particular response bubble, the corresponding read level would be at or near 0. By contrast, bubbles darkened by a mark will have read levels that fall near the high end of the read level scale. Erased marks usually fall between these two extremes.
Multiple choice academic examinations usually involve questions where there is exactly one correct answer per question. The common way to grade such an examination is to scan the response bubbles and identify the unique, darkest response bubble in the answer area for each question. That is, the darkest mark in a response bubble that is a sufficient discrimination level away from the next darkest mark is deemed to indicate the examinee's answer to the question. If such a mark is not found, the entire question is scored as not answered. The lighter marks corresponding to the same question are typically ignored.
This procedure works well for examinations where there exists only one correct answer per question, because it can reasonably be assumed that the unique, darkest mark is the examinee's intended answer. But when there is more than one correct answer per examination question or, in the context of survey questions, when the respondent wishes to choose either none or more than one of the possible responses, this procedure does not produce good results (or may require multiple scans for the same sheet). Because only the darkest of the response bubbles is identified, other response bubbles chosen by the examinee are not identified. Thus, intended responses may be missed. Similarly, a response bubble with an erasure may be misinterpreted, if an examinee intends to leave all response bubbles unchosen.
The inadequacies with this prior art procedure can be illustrated by way of example. FIG. 1 shows an answer sheet 100 with five response bubbles 101 for each question, usable for an academic examination where the examinee is given five possible answer choices for each question, and where there can be any number of answers (from 0 to 5) that are considered correct (or at least sufficiently "correct"). For each question, credit is given for each correct answer within each question. Assume answer choices "A," "C," and "D" are correct answers and answers "B" and "E" are incorrect answers to a particular question. Under one scoring scheme, an examinee who chose all three of the correct answers would be given credit for three correct answers, but an examinee choosing only one of the correct answers would receive credit for only one correct answer. Because the prior art procedure described above can only handle a single darkest mark and assumes all other response bubbles are unchosen (even if a lighter mark does appear), such a scoring scheme could not be implemented; the prior art provides no means for differentiating between an examinee who chose all three correct answers and an examinee who chose only one correct answer. Therefore, this prior-art scanning and recognition procedure does not produce the desired results.
One possible solution for this problem is to define a single fixed read level cut-off, whereby all response bubbles with read levels at or above the fixed read level cut-off are assumed to be intended responses (i.e., chosen by the examinee), and whereby all response bubbles with read levels below the fixed read-level cut-off are assumed not to be intended responses (i.e., left unchosen by the examinee). The single fixed read level is thus used to decide whether each response bubble is either intentionally chosen or intentionally unchosen. With this solution, however, it has been observed that inaccurate results are obtained because of the variation in response bubble read levels for intended responses. Read level variation can be caused by pencil wear, pencil lead type variations, or adjacent erasures, or by fatigue, carelessness, or haste on the part of the respondent. (See FIG. 1, in which answer areas for questions 1 through 6 show examples of response bubbles with differing degrees of darkness. Response bubble "A" for question 7 is fully darkened).
What is needed, therefore, is a method for accurately evaluating scannable forms for examinations and surveys that permits more accurate discrimination of response bubble markings when, for any given question, one or more than one response bubble or no response bubble may be chosen.